Electrodeposited chromium coatings are extensively employed across many industries, and can be plated from either hexavalent or trivalent baths. For many years the hexavalent bath has been used to produce so called hard chromium coatings, with good wear and corrosion resistance; however, these are quite temperature sensitive, and their contact and wear properties decline rapidly at elevated service temperatures. Further, chemical baths based on hexavalent chromium, which are highly toxic and oxidative, have detrimental effects on the environment and on the health of those working with them. In contrast, chromium plated from the trivalent state frequently contains metalloid alloying elements like C, which fundamentally change the evolution of the coating microstructure upon heating; unlike hard chromium coatings, such alloy deposits harden considerably upon heating. Cr—C coatings derived from a trivalent bath may have broad applications in elevated-temperature environments. As an added benefit, the health and environmental concerns about trivalent baths are dramatically lower than for hexavalent ones.
Despite the advantages of Cr—C alloy deposits, the range of temperatures for which these coatings are suitable remains limited (<600° C.). This range is useful for some machine or engine applications, but is insufficient for, e.g., hot metalwork tooling surfaces. For this reason, it is desirable to develop new coatings with desirable hardness and surface properties even after heating to ˜800 or 900° C.